This invention relates to an apparatus and method for uniformly coating selected portions of a rotating container with a liquid by a direct physical application of the liquid.
Coating containers with various liquid substances is widely practiced in the container manufacturing industry. The applied coatings can be merely decorative paints, or necessary coatings such as opaque paints or lacquers that provide protection to container contents from photodegradation. Coating a container with resinous layers that upon curing protect the container from corrosion, or with preparative fluids such as anti-static coatings or primer base coats that enable other forms of processing to occur, is also a common practice in the industry.
One method of coating containers known in the prior art is spray coating. A sprayer, which can be either a pressurized mist type or pressureless type, is used to impart a liquid coating to a rotating container. However, these types of spray devices are unsuitable for many purposes. The liquid spray has a tendency to spread outside the desired coating area, consequently wasting expensive fluids, providing uneven coating thickness, and detrimentally coating areas of the container with a contaminating liquid.
The dispersion of a liquid coating to areas outside the intended area of coating is of particular concern to the food and beverage industry. The containers having an open end are particularly susceptible to contamination of the interior of the container from stray dispersion of an airborne spray. This type of spray contamination can adversely affect both the safety and taste of foods or beverages placed in the contaminated containers.
Various expensive and inadequate means of alleviating these problems have been used by the container manufacturing industry. Fume hoods or pressurized air flow can be used to draw or direct liquid mists away from areas of the container that do not need a coating of sprayed liquid material. Spray shields can be used to physically or electrostatically stop sprayed droplets from contacting an inappropriate area of the container. Recovery and purification methods also provide a way of reusing fluids spray deposited on the wrong surface. However, these methods can be expensive to implement and operate, limiting their extensive use with many types of containers.
One method of eliminating some of the problems associated with spray coatings has been to directly apply the coating to the container with a foam applicator attached to a revolving belt. A spongy foam is coated with the liquid substance during one point in its revolution, and applies the liquid coating to the object at a later point in the revolution. The method relies on the flexible nature of the foam, which can be differentially compressed to remain in conformable contact with an object to be coated. (See U.S. Pat. No. 3,677,801 issued July 18, 1972)
However, although the previous method allows the complete liquid coating of any container that does not have irregularities sufficient in magnitude to prevent conformable deformation of the foam layer to match the container irregularities, it does not adequately allow the application of a uniform coating to any container. This method gives a liquid coating of non-uniform thickness because the spongy foam dispenses a varying amount of liquid to the surface of the object depending upon the changing compressive forces exerted by an irregular object against the foam. Furthermore, the method is not capable of selectively coating a selected portion of a container without using a complex system of multiple belts with associated mounted foams.
Another method of coating a container involves the use of a roller having a central axis of rotation parallel to the direction of the container movement. The roller is constructed of a dimensionally stable high grade steel with parallel striations or grooves inscribed in the roller. Each groove is capable of holding a certain amount of liquid that can be applied to a container passing over the rotating rod. The rod is partially immersed in a liquid bath to maintain a supply of liquid in the grooves. Application of the liquid occurs when the liquid contacts an aluminum can (See U.S. Pat. No. 4,275,097 issued June 23, 1981)
Although a uniform coat of liquid is applied to the container by the previous method, the cost in construction and maintenance of precision machinery is too high for many purposes. Expensive materials, precision machined to exacting requirements are needed for successful operation of this invention. The method also does not allow for the uniform coating of non-cylindrical containers, greatly limiting the potential use of the method.
It is accordingly an object of the present invention to provide a container coating apparatus capable of coating selected portions of a container with a liquid.
It is a further object of this invention to provide a container coating apparatus suitable for continuous industrial manufacturing operation, simple to operate and maintain and capable of being easily adapted for use with a variety of containers.
It is also an object of this invention to provide a container coating apparatus that does not significantly apply any liquid coating to areas that do not require or are adversely affected by the presence of a liquid coating, thereby limiting the amount of liquid necessary to coat an object and preserving the interior of the container from harmful contamination.
Another object of the invention is to provide a container coating apparatus that can uniformly apply a liquid coating of constant thickness to a container, thereby preventing an uneven or patchy coating of the container and also limiting the amount of liquid necessary to ensure a minimal thickness of the coating.